(1) Technical Field
This invention relates to a wafer orienting apparatus. More particularly, this invention relates to a wafer orienting apparatus for wafers having a notch on a periphery using mechanical motion only.
(2) Description of the Prior Art
The following six documents relate to apparatus dealing with positioning a notch or flat on a periphery of a semiconductor wafer to identify its orientation.
U.S. Pat. No. 4,970,772 issued Nov. 20, 1990 to Robert E. Steere, III shows a method for aligning semiconductor wafers in a wafer cassette by providing an alignment fixture for wafers having a notch in a periphery.
U.S. Pat. No. 5,205,028 issued Apr. 27, 1993 to Thomas E. Leonard describes a method which can align notched wafers and/or align wafers with flats with one another.
U.S. Pat. No. 5,516,732 issued May 14, 1996 to Christopher Fleggal describes a method of pre and post handling and treatment of wafers in a vacuum between wafer cassette modules and a multistation wafer processing machine.
U.S. Pat. No. 5,533,243 issued Jul. 9, 1996 to Takanobu Asano describes a notch position aligning device with a rotating/supporting mechanism to align a plurality of wafers in a predetermined direction and minimize contact between the target and other members.
U.S. Pat. No. 5,551,829 issued Sep. 3, 1996 to Mark J. Jerolimov et describes an orientation apparatus and method for aligning indexing notches of disk-shaped members, such as semiconductor wafers, with a flexible, non-particulating alignment rod which rotates until the indexing notches are registered with the alignment rod.
U.S. Pat. No. 5,662,452 issued Sep. 2, 1997 to Quincy D. Allison describes an apparatus and method for aligning indexing notches of disk-shaped members, such as semiconductor wafers, using friction between the circumferential surfaces of an alignment rod and the drive roller.
During various stages of semiconductor wafer processing, precise positioning of a wafer is critical. For example, a fabrication step that includes ion implantation requires that the orientation of the crystalline lattice of the semiconductor material be known. For another example, there must be a precise alignment of a semiconductor wafer relative to a reticle or photomask, if the reticule or photomask is to be used to pattern a conductive layer for forming signal paths along a previously fabricated circuit structure on the wafer.
Various types of cassettes have been provided for conveying a plurality of wafers, such as semiconductor silicon wafers, from one place to another. Wafers are formed with a notch in the periphery for identification purposes and subsequent alignment and other operations. In order to align such wafers in a cassette, it has been known to use a wafer orienting apparatus. The apparatus usually includes a cassette support means to receive a cassette containing a row of wafers as well as a roller to lift the wafers within the cassette and to rotate the wafers until the notch in each wafer comes into alignment (usually with a steel rod) and drops down.
Referring to FIG. 1, typically, asemiconductor wafer 10 will include both a wafer flat and an indexing notch 12 for positioning. A wafer flat or indexing notch 12 is an edge feature and is used to identify the orientation of the wafer 10. There are devices designed to align the flats of wafers 10, as well as xe2x80x9cnotch finders,xe2x80x9d devices which align the notches 12 of a semiconductor wafer 10 contained within a cassette 15.
Referring to FIG. 2, a schematic representation of the prior art showing the semiconductor wafers 10 with notched peripheries 12 in position in the cassette 15 with a pair of curvilinear walls which are sized to seat a wafer in an upstanding manner. FIG. 2 also shows the prior art rotating stainless steel rod 14, which acts as an aligning roller.
Referring now more particularly to FIG. 2 of the prior art, the notch finder may have a small diameter stainless steel rod 14 having a coating of polyvinlydenefloride. When the cassette 15 is positioned on the device, the edges of the wafer in the cassette 15 contact the stainless steel rod 14. Rotation of the stainless steel rod 14 causes the wafers 10 to rotate within the cassette 15. When a notch 12 of a rotating wafer 10 reaches the stainless steel rod 14, the notch 12 allows for the wafer 10 to drop slightly onto the rod 14. The stainless steel rod 14 continues to rotate, but the notch-to-rod registration prevents further rotation of the wafer 10. Within a relatively short time, all of the wafers 10 in the cassette 15 have been aligned.
In the prior art of FIG. 2, once the wafer 10 has been placed in the cassette 15, a minimum of time and effort is required to bring about an alignment of the notches 12 of the respective wafers 10 in the cassette 15. The cassette 15 is of conventional structure. The wafer 10 is rotated by the rotating stainless steel rod 14 until the notched periphery 12 comes in contact with the rod 14, falling down into alignment and ceasing to rotate
A notch finder may also include a mechanism for uniformly rotating the wafer notches after an alignment operation. Rollers may be positioned on opposite sides of the stainless steel rod out of contact with the wafers during the notch alignment operation. Then, the rollers may be moved upwardly to contact the wafer edges, lifting the notch away from the stainless steel rod. The rollers can then be rotated to relocate the aligned notches to a desired position.
Conventional notch finders operate well for their intended purpose. However, there are concerns relating to the operation of the conventional notch finders. As previously noted, the stainless steel rod continues to rotate after the first notch is brought into registration with the rod. Rotation of the stainless steel rod against the stationary edges of the notch generates noises that can be disruptive to persons in the vicinity of the notch finder. More importantly, the relative rotation between the stainless steel rod and the semiconductor wafer may generate particles that settle on the surface of one or more of the wafers. Particulate contamination will adversely affect the manufacturing throughput of the semiconductor fabrication process.
It is the object of the present method to orient semiconductor wafers having a notched periphery using mechanical motion only. Another object of the invention is to provide a method for aligning wafers which is simple, inexpensive and effective and has applications potential for any tool that does not have a built-in wafer orientor. Another object of the invention is to simplify aligning a plurality of wafers by joining together, for example, 25 such assemblies and thus aligning 25 wafers at the same time.
Another object of the invention is to eliminate particulate generation during the alignment procedure which can greatly undermine the efficiency of the semiconductor, and to eliminate damage to the wafers by allowing the aligner to function in a vertical position for loading and then turn down into a horizontal position for processing.
Yet another object of the invention is its easy modification to accommodate wafers of any size, provided they are notched, by simply modifying the length of the elbow arm.
In accordance with the objects of this invention, an apparatus for aligning a plurality of semiconductor wafers, having an orientation notch and contained in a wafer cassette, is achieved.
The plurality of semiconductor wafers are contained in a cassette that is conventionally used in the industry. The wafers are equidistantly spaced within the cassette so that the wafers do not make contact during storage, transportation or handling.
In the preferred embodiment, a plurality of wafer orientation mechanisms coinciding with each wafer position of a cassette, are placed as an assemblage over a cassette containing a plurality of wafers. The wafer orientation assembly is first secured to the cassette and then inverted allowing the weight of each wafer to contact the orientation mechanism.
A wafer orienting apparatus for aligning a plurality of semiconductor wafers each of which has a v-notch formed on its outer periphery. The apparatus includes a cassette process carrier for supporting the plurality of wafers in parallel wafer supporting slots and wafer supporting means engaging the periphery of each wafer in an individual slot with the central axis of all wafers in coaxial alignment. A supporting platform is placed over the cassette for supporting the wafers in an inverted position in which the wafers are substantially vertical and biased by their own weight against a multiplicity of orienting mechanisms. The orienting mechanisms are arranged to correspond to each wafer position within the cassette. The plurality of orienting mechanisms are integrated with the supporting platform so that all wafers within the cassette can be aligned during this aligning process. Each orienting mechanism includes a v-block that is mounted substantially normal to and in vertical alignment below each wafer axis, and has two degrees of vertical freedom relative to the supporting platform with spring means for biasing the apex of the v-block towards the peripheral edge of the wafer. The v-block is positioned between a pair of supporting friction drive rollers. The rollers are in a first position for engaging the periphery of the wafer and with means for rotatively driving each roller to impart rotation to the wafer, thereby, with time, aligning the notch to the v-block thus permitting the apex to be urged into the aligned notch. Because the rollers are connected by an assembly to the v-block, they move downwards, away from the wafer, when the v-block moves upwards, and the wafer, now in alignment, ceases to rotate.